WO2004027301A1

WO2004027301A1 - Safety valve

Info

Publication number: WO2004027301A1
Application number: PCT/IT2003/000548
Authority: WO
Inventors: Roberto Serpilli
Original assignee: Lacerta Srl Con Unico Socio
Current assignee: Lacerta Srl Con Unico Socio
Priority date: 2002-09-18
Filing date: 2003-09-12
Publication date: 2004-04-01
Anticipated expiration: 2005-03-18
Also published as: AU2003265166A1; ITAN20020043A1

Abstract

The present invention refers to a safety valve for pressurised fluid dynamic installations, that comprises a threaded tubular stem (1) inserted into the valve-body (3) obtained by a moulding process using a mould in which the threaded tubular stem is loaded.

Description

Safety valve

The present patent application for industrial invention refers to a safety valve for pressurised fluid dynamic installations, and in particular for reservoirs with pressurised fluids.

Safety valves are normally used in plugs of reservoirs with pressurised fluids that undergo high increases in temperature and, therefore, pressure.

This type of reservoirs must be necessarily provided with a safety valve to maintain the internal pressure below the threshold value and prevent the reservoir from suffering stresses higher than permitted, according to its dimensions. Safety valves are often incorporated in the reservoir plug, such as in the case of small boilers for steam irons, espresso coffee machines, steam cleaning or degreasing devices.

Safety valves are generally composed of a monolithic brass body, provided with an externally threaded lower stem with tubular configuration, whose internal conduit ends in the valve-body with hexagonal head, provided with a ventilation chamber with a spring that pushes the obturator disk against the bottom wall of the ventilation chamber to hermetically close the communication hole between chamber and stem. The spring is compressed by a calibration screw tightened into the opening of the ventilation chamber, which is suitably provided with threaded internal wall. The calibration spring allows for compressing the spring to oppose the pressure exercised by the fluid under the disk, being evident that when the fluid pressure exceeds the spring pressure, the obturator disk is lifted up, thus allowing the pressurised fluid to flow outside through the ventilation hole located on the chamber wall.

The valve stem must be tightened to the reservoir and in order to guarantee good seal, a packing ring is inserted on the stem and stopped at the end of the threaded section of the stem, where a shoulder is provided to hold and press the ring down. In order to ensure effective, uniform pressing of the ring, a washer with arch-shaped section is positioned between the shoulder and the ring, perfectly adhering to the ring.

To ensure safe removal of the plug, safety valves are normally provided with a small ventilation hole also along the threaded section of the stem, so that, before loosening the plug completely, the pressure of the fluid in the reservoir can descend to values close to atmospheric pressure, thanks to the spontaneous flow of the fluid through the small ventilation hole, as soon as the same disengages from the threaded hole of the stem. Although traditional safety valves are very effective in terms of protection against possible injuries, it must be noted that the same are not advantageous in terms of production costs.

In fact, this type of valves is obtained from a brass bar, which is machined on the external cylindrical part of the ventilation chamber and the threaded stem with lower diameter, in order to create a shoulder between ventilation chamber and stem for the washer used to press the ring inserted on the threaded stem.

Once the turning process of the external surfaces of the valve has been completed, including the threading and axial drilling of the stem, the part must be placed on the counter-mandrel of the lathe to realise the internal turning of the valve head, where the ventilation chamber with threading for the calibration screw must be realised.

Once the surfaces have been turned, the radial drilling of the valve in the ventilation chamber and in the threaded stem is performed to create the ventilation holes.

The manufacturing process of safety valves is considerably expensive in view of prolonged machining time, downtime to transfer the part from the mandrel to counter-mandrel, and extended drilling operations.

Finally, the excessive waste of material during the turning process of brass bars must be noted, it being necessary to excavate the bar internally to create the ventilation chamber and turn it externally to create the threaded stem with lower section than the brass bar section. The present invention has been devised to overcome the problems related to excessive production time and cost of safety valves.

The valve of the invention is composed of two parts, namely a valve-body obtained by a moulding process, preferably made of plastic material, and a threaded metal stem obtained by a turning process, preferably made of brass.

The valve-body contains a circular ventilation chamber with smooth internal walls, closed by a plug which is forced onto the opening of the chamber, by pressing it suitably above an elastic calibration element that closes the obturator on the bottom of the ventilation chamber. One side of the brass tubular stem ends with a part having a non-circular section, which is inserted in the valve-body in order to mutually hold the two elements in place.

The fact that the valve-body is obtained from a moulded piece, separate from the threaded stem, has the following advantages. Firstly, turning time is reduced, since the only turning operation refers to stem threading and can be carried out without placing the part on the counter- mandrel of the lathe.

Secondly, the quantity of wasted material in the turning process is reduced, since the section of the original hexagonal bar is slightly larger than the stem and is no longer necessary to excavate the ventilation chamber on the head of the valve-body.

Additional reduction of costs originates from the elimination of the boring operation of the valve-body to realise the ventilation holes, which are obtained when moulding the valve-body. Another advantage in terms of production costs derives from the possibility of shaping the valve-body in such a way as to obtain a shaped shoulder for the ring during the moulding process, thus eliminating the costs related to the presence and mounting of the washer on the valve.

Moreover, the new safety valve of the invention lacks the calibration screw, which is replaced by the less expensive plug, whose operation mode contributes to reducing calibration time for the screw.

For major clarity the description of the invention continues with reference to the enclosed drawings, which are intended for purposes of illustration only and not in a limiting sense, whereby:

- Fig. 1 is a section of the valve of the invention with an axial plane;

- Fig. 2 shows the stem of the valve of the invention; and - Fig. 3 is a section of the stem of the valve of the invention with axial plane A-A of Fig. 2.

With reference to the aforementioned figures, the valve of the invention is composed of a tubular stem (1) made of metal and externally provided with a first threaded section (1a) and a second unthreaded section (1 ) divided by an annular groove (1c) that houses the packing ring (2).

The stem (1) is contained in a housing located in a pressurised fluid dynamic installation.

The unthreaded section (1b) ends with a non-circular flange (1d), while the threaded section (1a) has a small ventilation hole (1e) that ends in the internal conduit (1f).

The valve-body (3) is made of plastic material by means of a co-moulding process on the section (1b) of the stem (1) and contains a ventilation chamber (3a) with smooth walls and circular section, provided with radial ventilation holes (3b) and closed by a plug (4) forced on the opening (3c) of the chamber.

The chamber (3a) houses an elastic calibration element (5) and a obturator (6) that closes the hole on the bottom wall of the ventilation chamber which provides communication between the ventilation chamber and the internal axial conduit (1f) of the stem (1). The unthreaded section (1b) of the stem (1) is inserted, together with the anchoring flange (1d), in the valve-body (3), whose ending section is located immediately above the annular groove (1c), so that the ending section creates a shoulder to hold and press the ring (2) down. The ending section is provided with shaped profile suitable to surround the ring (2) that is housed in the annular groove (1c).

The elastic element (5) is calibrated by means of the plug (4) which is forced onto the opening (3c) until the compression of the elastic element (5) reaches the established calibration value.

At the end of the insertion travel in the opening (3c), the plug (4) is firmly held in place because of the forced matching; in any case, for total safety reasons, the plug (4) can be permanently held in place with welding or riveting, in order to avoid back travels. In this way the valve-body (3) and the plug (4) create a single piece.

As regards the production process of the valve of the invention, it must be noted that, once the stem (1) has been manufactured, the same is loaded in the mould of the valve-body (3), which protrudes from the mould with stem (1) and ventilation chamber (3a) with radial ventilation holes (3b).

Claims

1) Safety valve for pressurised fluid dynamic installations, of the type composed of a valve-body (3) and a tubular stem (1) that engages a housing located in the installation during operation and has an internal axial conduit (1f) that ends into a ventilation chamber (3a) provided with ventilation holes (3b) and obtained inside the valve-body, which houses an adjustable system (5) that actuates on an obturator (6) used to close the communication hole between the ventilation chamber (3a) and the axial conduit (1f), valve being characterised in that the stem (1) and the valve- body (3) are separate pieces. 2) Safety valve as defined in claim 1, characterised in that the stem (1) and the valve-body (3) are made of different material.

3) Safety valve as defined in claim 2, characterised in that the valve-body (3) is made of plastic material.

4) Safety valve as defined in claim 3, characterised in that the valve-body (3) is obtained by means of a co-moulding process in a section of the stem

(1).

5) Safety valve as defined in any of the preceding claims, characterised in that the stem (1) is made of metal.

6) Safety valve as defined in any of the preceding claims, characterised in that the adjustable system comprises elastic elements (5) that act on the obturator (6) and a plug (4) forced in a housing of the valve-body (3) in order to actuate on the elastic elements (5); the travel of the plug (4) being defined along the longitudinal axis of the internal hole (1f) and made until the established calibration value has been reached by anchoring it to the valve-body (3), thus obtaining a single piece with the plug (4) and the valve-body (3).

7) Safety valve as defined in any of the preceding claims characterised in that the stem (1) externally has a first threaded section (1a) and a second unthreaded section (1b) divided by an annular groove (1c) that houses the packing ring (2). 8) Safety valve as defined in claims 4 and 7, characterised in that the stem (1) has a short part with non-circular section in the section contained in the valve-body (3).

9) Safety valve as defined claim 8 characterised in that the valve-body (3) ends with a base section located immediately above the annular groove (1c) and having an external shaped profile capable of surrounding the ring (2).